Desalinization of aqueous solutions



United States Patent 3,419,492 DESALINlZATION OF AQUEOUS SOLUTIONSHerman S. Bloch, Skokie, Ill., assignor to Universal Oil ProductsCompany, Des Plaines, Ill., a corporation of Delaware No Drawing.Continuation-impart of application Ser. No. 376,561, June 19, 1964. Thisapplication Sept. 5, 1967, Ser. No. 665,226

8 Claims. (Cl. 210-32) ABSTRACT OF THE DISCLOSURE A composition for usein a processing scheme designed to separate water from an aqueous saltsolution-e.g. sea water. The compounds are water-insoluble polymers ofaliphatic and/or aromatic, ethylenically unsaturated amino acids whichare cross-linked with a ketone and/or an aldehyde. The acid-actingradical of the amino acid is selected from the group of sulfonic andcarboxyl, and is substituted on a carbon atom separted from the carbonatom bearing the amino group by not more than five intervening carbonatoms. Preferred compositions are those polymers which are cross-linkedby formaldehyde and/ or acetole-i.e. an aromatic ethylenicallyunsaturated carboxylic amino acid cross-linked by acetole.

RELATED APPLICATIONS The present application is a continuation-in-partof my copending application Ser. No. 376,561, filed June 19, 1964, nowUS. Patent No. 3,351,549, issued Nov. 7, 1967, all the teachings ofwhich patent are incorporated herein by specific reference thereto.

APPLICABILITY OF INVENTION This invention involves the process ofseparating water from an aqueous solution of a salt by removing both thenegative and positive ions of the salt from the solution, in whichprocess the feed stock is contacted with a particular ion-retentionagent or resin containing polar radicals selected from certain ionicgroups which entrap the salt ions by a retention mechanism involvingmutual attraction between the oppositely charged polar groups residingrespectievly on the resin and in the ionized salt. The electricalcharges of the polar groups in the resin in efiect neutralize thenegative charge on the anion, and the positive charge of the cation inthe salt. More specifically, the invention concerns particularion-retention agents to be employed in increasing the water content ofan aqueous solution by the withdrawal and retention of the ioniccomponents of a salt in said solution, to form a product solution, thesalt concentration of which may be reduced substantially to nil. By aspecial desorption treatment of the spent ion-retention material, a saltconcentrate may be produced as either the primary or secondary product.

The organic compositions utilized in the present process as the ionretention agents, acquire a relatively more spent condition after theyhave absorbed a quantity of salt ions from the aqueous salt solutionsupplied to the process as feed stock, the quantity of salt retained bythe adsorbent being dependent upon the temperature of the feed solutionand the concentration of salt in solution which is in equilibrium withthe salt adsorbed by the ion retention agent. The spent composition maythereafter be restored to its active or regenerated form by contactingthe spent composition with water (referred to herein as a desorbent) inwhich the salt concentration is below the level at which the salt insolution is at equilibrium with the salt retained on the resin duringthe preceding ion-retention stage of the process cycle.

3,419,492 Patented Dec. 31, 1968 The absorbed salt ions in thecomposition tend to migrate from the spent ion retention agent into theaqueous desorbate phase. The salt concentration in the aqueous desorbentphase rises in direct proportion to the regeneration temperature and thesalt content of the spent composition.

When ion retention agents of the present invention are employed as anintegral part of a salt recovery process, the effiuent desorbate streamcomprises an aqueous salt concentrate from which the remaining water maybe evaporated or removed by other means, where the salt, in a dehydratedform, is the desired end product of the process. The recovery of a saltconcentrate from the spent ion retention agent during the desorptionstage of the process cycle, therefore, is in effect a dewatering processon the feed stock solution as the first step in producing the dry oranhydrous salt by further removal of the remaining water from thedesorbate concentrate. By thus increasing the concentration of salt inthe saline solution as a result of the desorption of salt from the spention retention agent in the sequence of steps comprising the presentprocess, a major portion of the water present in the relatively diluteaqueous solution comprising the original feed stock is therebyeliminated prior to the final stage of preparing the dried salt product.The present method of desalinization, therefore, reduces the quantity ofwater which must ultimately be evaporated from the feed stock solutionto recover the solute in an anhydrous form. The process, to which thepresent invention is applied, accordingly provides a means for effectingsuch initial reduction in the proportion of water in the feed stocksolution more effectively and more economically than processes of theprior art, such as evaporation, ion exchange, electrophoresis and otherconventional procedures.

One of the principal and most useful applications of the presentinvention, in a process for recovering water from an aqueous saltsolution, resides in the separation of substantially pure, ion-freewater from a feed stock salt solution for the sake of the watercomponent itself. For this purpose, the feed stock solution utilized forsuch water recovery is preferably a solution of minimum salt content;since the capacity of the ion retention agent and its efficiency in thedesalinization process is inversely proportional to the concentration ofsalt in the feed stock solution, the yield of water per unit of fedlstock increases in inverse proportion to the salt content of the fedstock. This adaptation of the process provides a means for producingpotable water at a stage in the growth of world population when thepresent sources of water are rapidly becoming inadequate. New sources ofsupply are being actively sought throughout much of the world, not onlyfor purposes of direct human and animal consumption to sustain life andmaintain sanitary standards, but also for the irrigation of plant lifeand for the vast number of other uses requiring potable water. Althoughsea Water is readily avalable in virtually unlimited quantities and maybe pumped inland for substantial distances to available heatingfacilities and to sources of electric power and other forms of energy,the recovery of potable water from sea water by presently known methodspresents a formidable problem of cost. The separation of Water from itssaline solutions, using such facilities as distillation, freezing,membrane dialysis, ion exchange, etc., involves the con-sumption oflarge quantities of heating, cooling and electrical utilities orrequires such large outlays of capital for equipment that the per unitcost of potable water (containing not more than 500 ppm. by Weight ofsolids) produced by such means from sea water generally exceeds theupper limit of acceptable cost which is generally about 40 cents perthousand gallons for drinking water purposes and about 19 cents perthousand gallons for irrigation purposes. Except for special uses ofpotable water which would justify a cost exceeding such limits, theforegoing conventional procedures have been generally discredited asreasonably feasible means for the production of potable water on a largescale.

On the other hand, in the aforementined use of the present process forthe production of salt concentrate from which the anhydrous salt may berecovered, for example, by further removal of the remaining water fromthe concentrate by distillation or by other means, the feed stock to thedesalinization process is preferably as concentrated as feasiblyavailable, and its desirability for this purpose increases as theconcentration of salt in the feed solution increases or is inverselyproportional to the ratio of water to salt in the solution.

The present process, employing the ion retention agents of the presentinvention, is operated on a repeating and alternating cycle of heatingand cooling, comprising initially absorbing ions from the salt solutionon the ion retention agent at the coolest temperature of the cycle,followed thereafter by removal or desorption of the ions from the spentretention agent at the relatively elevated temperature maintained duringthe regeneration phase of the cycle. The resulting, relatively largevariations in temperature would normally involve the expenditure ofsubstantial quantities of heat to effect the large temperature swingbetween the absorption and regeneration stages of the process; however,the heat involved in effecting such temperature swing consists entirelyof sensible heat and the resulting net consumption of heat for thispurpose is much less than that required to provide the latent heat ofvaporization or the latent heat of fusion in operating a desalinizationprocess by either of the evaporation or freezing mechanisms involved inprocesses of desalinization in the prior art. Moreover, the use of thepresent process flow, which involves a heat exchange principle in whichthe heating and cooling capacity of the several process streams arealternately stored in, and thereafter recovered from the resinous ionretention agent, provides an especially advantageous application of theprocess flow described in US. Patent No. 2,985,589, issued to D. B.Broughton et al., whereby a major proportion of the heating and coolingdemands of the process can be re covered thereby reducing the ultimatecost factors involved in the process to substantially nil. Through suchspecial uses of the heat exchange capacity of one of the phases presentin the process flow in the present method, the recovery of the watercomponent and/ or the recovery of the salt component of an aqueoussaline solution may be accomplished with only nominal consumption ofheating and other utilities.

OBJECTS AND EMBODIMENTS In one of its embodiments, this inventionrelates to a process for the desalinization of an aqueous salt solutionwhich comprises contacting said solution at a relatively low datumtemperature with an ion retention agent comprising an organiccomposition containing acid-acting and base-acting polar groups insubstantially equal number, substituted on carbon atoms in the molecularstructure of the composition in an arrangement of said groups whichprovides a succession of alternating acidic and basic substituents onthe carbon atom skeleton, whereby substantially each acid-acting groupis adjacent to a base-acting group to form a dipolar aggregate which, oncontact with said solution, retains the electropositive andelectronegative ions of the salt in solution, and forms a resulting ionretention agent at least partially spent with respect to its capacity toretain additional charged ions, and withdrawing at said datumtemperature from the ion retention agent containing absorbed thereon thesalt ions originally present in said solution a water product having alower concentration of salt than said solution.

Another embodiment of the present invention concerns a means forrestoring the activity of the ion retention agent for further use incontacting additional feed stock solution which comprises contacting theion retention agent containing a'bsonbed salt with water at atemperature relatively more elevated than said datum temperature andremoving at said elevated temperature a desorbate effiuent of highersalt concentration than said feed stock solution from a resultingregenerated ion. retention agent.

Other embodiments of my invention relate to specific ion retentionagents, special conditions of temperature and salt concentrations atwhich the process operates and other specific aspects relating to theprocess, and especially the ion retention agent upon which the processis based. These will be referred to in greater detail in the followingfurther description of my invention.

For example, a specific embodiment encompassed by my invention, providesan organic substance having heatreversible ion retention capacity andbeing the composition formed by treating the polymer of an ethylenicallyunsaturated carboxylic amino acid in which the number of amino acidmonomer units in the polymer is sufficient for said polymer to bewater-insoluble, with a ketone at condensation reaction conditions; saidsubstance further characterized in that (a) said ketone reacts with theamino group to form a composition having a higher melting point thansaid polymer, and (b) the carboxyl group is substituted on a carbon atomseparated from the carbon atom bearing the amino group by not more thanfive intervening carbon atoms.

In another specific embodiment, the present invention is directed towarda process for the desalinization of an aqueous solution of a dissolvedsalt which comprises contacting said solution at a low datum temperaturewith an ion retention agent comprising a water-insoluble compositioncontaining an acid-acting radical selected from the group consisting ofsulfonic and carboxyl and a baseacting amino radical, cross-linked by acarbonyl compound selected from the group consisting of aldehydes andketones, each of said acid-acting and base-acting radicals beingsubstituted on carbon atoms in the molecular structure of thecomposition separated by not more than five intervening carbon atoms,whereby substantially each acid-acting group adjacent to a base-actinggroup forms a di-polar aggregate which on contact with said solutionwithdraws the electropositive and electronegative ions of the salt fromthe solution and forms a resulting complex between the acid-acting andbase-acting radicals in the ion retention agent with the electronegativeand electropositive ions of said salt and withdrawing at said datumtemperature from the ion retention agent containing absorbed thereon thesalt ions originally present in said solution a water product in whichthe concentration of salt is less than the salt concentration of saidsolution.

SUMMARY OF INVENTION The desalinization of aqueous salt solutions inaccordance with the process of this invention is dependent upon theeffectiveness of a water-immiscible composition referred to herein as anion retention agent, or resin, which is capable of forming anaddition-type complex with the salt component of the aqueous solution.By contacting the feed stock solution with the compositions encompassedby the present invention, the salt ions in solution are retained in aseparately recoverable phase, thereby extracting the latter from thefeed stock solution and leaving, as the other phase, water of greatlyreduced salt content. The process, accordingly, is dependent upon thecapacity of the ion retention agent for retaining the salt ions in anabsorbed state on or in the composition, as water of reduced saltcontent, at the lowermost or datum temperature provided by the process,is withdrawn from the spent resin as non-absorbed retfinate product. Thefeasibility of the present desalinization process as an economicallyjustifiable means for producing a product of low cost is also dependentupon the ability of the composition to release its absorbed salt ions,extracted from the aqueous feed stock solution, without the expenditureof large inputs of energy, or by other costly procedures for restoringthe ion retention agent to its active or regenerated state. An integralphase of the over-all process is the release of the salt ions from thespent ion retention agent at conditions which disrupt ionic equilibriumbetween the ions present in the surrounding fluid phase and the ionsalready present in an absorbed state on the ion retention agent, wherebythe ions present in the ion retention agent migrate from the resin tothe surrounding fluid phase. Such disruption of ionic equilib rium iseffected either by increasing the temperature of the surrounding fluidphase (the aqueous desorbent) to a level more elevated with respect tothe initial datum temperature, by reducing the saltcontent of thesurrounding fluid phase below the salt concentration of the initial feedstock solution supplied to the process, or by combining both of theaforementioned means in a unitary regeneration procedure to promote therate or the degree of salt removal from the ion retention agent by themutually additive effect of both temperature and the disruption of ionicequilibrium. Although, presumably, the aqueous feed stock solution canbe utilized as the source of water to effect desorption of the salt ionsfrom the spent resin, at a more elevated temperature than the level atwhich salt absorption took place, the absorbed ions are more nearly inequilibrium with the ions in the desorbent solution contacted therewithso that the resulting reduction in the rate of ion transfer from the ionretention agent into the desorbent, when. using the feed stock solutionas the source of desorbent, is lower than when using deionized water ora solution of lower salt content than the feed stock. A stepwisedecrease in the salt content of the dcsorbent stream contacted with thespent ion retention agent, for example by first charging feed stockheated to the elevated temperature of the -de sorbent into thedesorption zone, followed thereafter by contacting the resulting,partially regenerated ion retention agent with deionized water at theelevated desorption temperature is advantageous in that the procedurereduces the total quantity of deionized water required for thedesorption o-r regeneration stage of the cycle.

The foregoing heat-reversible, ion-retaining properties of the presention retention agents enable the salt ions to be desorbed from the spentcomposition during the regeneration stage to thereby supply aregenerated resin for repeated use of the same composition in a cyclicflow arrangement for further removal of ions from the feed stocksolution at a more downstream portion of the cycle.

The ion retention agents utilized herein to remove dissolved salts fromaqueous feed stock solutions are members of a group of materials whichare capable of forming a reversible complex with both theelectronegative and the electropositive ions of the salt component ofthe solution. The designation of these compositions, as ion retentionagents, is thus an indication of their function in the present process,the agent in each case acting essentially as a means for withdrawing thesalt ions from the solution and retaining the salt in the form of anaddition complex with the composition in a sufficiently tenaciouscombination and for a sufiicient length of time to permit the withdrawalof salt-depleted water from the downstream outlet of the ion retentionzone. The ion retention zone of the process cycle must therefore containsufficient ion retention capacity in the form of the water immiscibleion retention agent to remove all of the salt ions from the feed stocksolution at the feed stock flow rate, and at the temperature and saltconcentration at which the feed stock is supplied to the process.

The composition employed herein as the ion retention agent must alsohave the aforementioned property of reversibly releasing the salt fromits addition complex with the composition as the temperature of thesurrounding aqueous phase is increased beyond the ionic equilib riumtemperature for the aqueous phase in contact with the spent composition.These properties characterize generally certain macromolecular weightsolid resinous or resin-like materials which qualify as ion retentionagents in the present process.

Compositions capable of functioning as ion retention agents of thepresent invention contain radicals having both base-exchange andacid-exchange activity, which, because they are spaced apart in the samemolecule, act in their individual capacities as electronegative andelectropositive ion traps, but which, because of their close proximityin the same molecule, form dipolar ionic groups or internal salts of aclass referred to in the art as Zwitter ions. A common form of theacid-base or dipolar ion exchange groups are the amino acids, whichstructurally may be considered as the disubstituted ammonium salts ofcarboxylic or sulfonic acids having aliphatic, carbocy-clic orheterocyclic aromatic or naphthenic structures supporting the amino andacid groups as substituents. The essential, reactive unit present in thestructure of the ion retention compositions of this invention may alsobe visualized as acid-base compositions of substantially isoelectricneutrality, but which, because of the intervention of at least one, upto about five carbon. atoms between the carbon atoms bearing the acidand base groups re spectively, do not react to form rigidly stableinternal salts via neutralization of the amino groups with thecarboxylic and/or sulfonic acid groups present as substituents withinthe compositions. As heretofore indicated, the acid portion of thedipolar ion group may be present as a carboxylic or sulfonic acidradical, the former in partially or completely hydrolyzed proteins(i.e., as a monoor polyamino acid) and the latter in certain syntheticcompositions containing the sulfonic acid radical (-SOgH) and the aminobase radical in the form of a polymeric ammonium or alkyl ammoniumsulfonate composition. Thus, the dipolar ion units present in thestructure of the compositions herein utilized as ion retention agentsinclude both the amino-carboxylic acids and the amino-sulfonic acids ashomogeneous or heterogeneous compositions.

The present compositions utilized as ion retention agents may alsocontain a predominance of either amino groups or acid groups in anyparticular structure and, therefore, are not necessarily wholly neutraland may have a pH either greater or less than 7.0. In order to preventinternal salt formation between the amino and acid groups contained inthe structure of the dipolar ion, these groups, respectively, aresubstituted on carbon atoms separated by one or more, up to about five,intervening carbon atoms and more preferably, they are separated by fromone to three carbon atoms between the carbon atoms bearing the amino andacid groups, respectively. The effective field of ion retention activityprovided by the electropositive and electronegative ionic groups in theion retention agent, thereby corresponds approximately to the field ofthe electropositive and electronegative ions of a mc1 lecule of ionizedsodium chloride or other inorganic S8. t.

The present ion retention agents effect the removal of salt ions fromaqueous solutions by means of a mechanism illustrated in the followingequation for a resin containing an amino group and a carboxylic acidgroup acting on sodium chloride as an illustrative example:

where R is selected from the group consisting of hydrogen, alkylcontaining from 1 to 5 carbon atoms, phenyl, benzyl and alkylphenyl, atleast one of said R groups being hydrogen. In accordance with themechanism of the ion retention process involved in the presentinvention,

the electropositive ammonium ion, existing in the molecular structure ofthe ion retention agent, exerts an attractive effect on theelectronegative chloride ion of sodium chloride present in the aqueoussolution; simultaneously the electronegative carboxyl group present inthe ion retention agent exerts an attractive effect on theelectropositive sodium ion of the sodium chloride existing in a freelymobile form in the aqueous solution. At the relatively low datumtemperature utilized for treatment of the aqueous feed stock solutionduring the ion retention phase of the process, the respective positiveand negative sodium and chloride ions of the salt migrate to theattracting, oppositely charged ionic groups present in the ion retentionagent, both ions being loosely held within the ionic field of the firmlyheld positively and negatively charged acidacting and base-acting groupscomprising the ion retention agent. The mobile salt ions, however, areheld in the dipolar complex only as long as the ambient temperature doesnot rupture the bonds between the salt ions and the antipode groups inthe ion retention agent. At the elevated desorption temperaturesprovided in the present process the bonds existing between theoppositely charged ionic groups in the salt and in the ion retentionagent are ruptured, regenerating the free electropositive ammoniumradical and the electronegative carboxyl or sulfonic radical of the ionretention agent, simultaneously releasing the sodium chloride as amobile ionic entity into the aqueous phase surrounding the ion retentionagent. The proportion of regenerated to total resin or the ratio of freecarboxyl or sulfonic acid groups and amino base radicals to totalcarboxyl plus carboxylate, sulfo plus sulfonate, and amino plus ammoniumradicals increases as the temperature of the treating agent increases,(depending upon the composition of the ion retention agent, theconcentration of salt in solution and the identity of the salt), exceptthat, at certain threshold temperatures, generally substantially belowthe boiling point of the aqueous desorbent, the treating agent isessentially wholly regenerated at any concentration of solute in thedesorbent. What is true for the detention of the sodium and chlorideions of sodium chloride, one of the more common components of sea water,is also generally true for other metal-derived electropositive andelectronegative ions of other salts, such as the electropositive calciumand magnesium ions of calcium chloride and magnesium chloriderespectively, or the electropositive potassium and lithium and theelectronegative sulfate ions of potassium and lithium sulfates as wellas the ionic radicals of various other salts which are soluble in Water.

The treating or ion retention agents which contain amino acid dipolar orZwitter ion groups as the active ion-retention centers present in theirmolecular structures are provided by a variety of materials which may bederived from naturally-occurring sources, or prepared synthetically bypolymerization of monomers containing one or more amino groups andcarboxylic and/or sulfonic acid groups per molecule. For example, bothamino and carboxyl groups are present in or derived from water-insolubleproteins or proteinaceous materials, such as casein, leather, animalhair, soya bean proteins, nut proteins and the like, generally havingmolecular Weights above 3000, up to about 75,000. Some of the preferrednaturally occurring proteins and protein-conversion products areobtained by partial enzymatic or acid hydrolysis of a natural protein inthe presence of a weak aqueous acid solution which reduces the molecularweight of the protein and hydrolyzes a portion of the carboxyamidelinkages present in the molecular structure of the protein to the freeamino acids.

In a process for treating a liquid feed stock utilizing the treatingagent in solid particle form, it is, of course, a necessary requirementof the solid thus used that it remain in the solid phase during theprocess and that it continue to be essentially insoluble in the aqueousphase at either the ion retention stage of the process or the desorptionstage thereof. Accordingly, materials which tend to melt or which tendto dissolve in the aqueous phase at the relatively elevated desorptiontemperatures are preferably pretreated with a modifying agent prior touse in the process in order to convert the ion retention agent into awater-insoluble and/or a refractory material to render the particularsubstance more useful and more suitable for the present ionretention-desorption process cycle. For this purpose, the material usedas the ion retention agent, when derived from a substance of low meltingpoint or of high water solubility is desirably pretreated prior to usewith a reagent including low molecular weight aldehydes, such asformaldehyde, acetaldehyde (or its trimer: paraldehyde), glyoxal,acrolein, propionaldehyde, crotonaldehyde, or other aldehydes containingup to about 5 carbon atoms per molecule or with an acylating agent suchas acetyl chloride, formyl chloride, propionyl chloride, thecorresponding bromide analogs or other acylating agents, such as theacid anhydrides which substitute the involved acyl radical into some ofthe resident free amino groups present in the monomer, replacing ahydrogen atom of the amino group and converting the proteinaceousmonomer to the corresponding condensation product with the aldehyde oracylating agent, having a higher melting point and lower watersolubility than the unmodified monomer. The preferred members of theabove modifying reagents are formaldehyde, formyl chloride, and formylbromide because of their high activity and the modified product producedtherefrom possesses many of the physical and chemical properties whichare desirable for ion retention agents used for this purpose. Thecondensation reaction between the aldehyde or other acylating agent andthe protein-like ion retention agent involving at least some of the freeamino groups present in the substance, and especially the amino groupsreleased by acid hydrolysis from the amide or ammonium salt is effectedand promoted by caustic or a base, such as a dilute solution of sodiumhydroxide, potassium hydroxide, sodium carbonate, lithium hydroxide,etc., and at temperatures of from about 20 to about C., the condensationproduct generally separating from the aqueous phase as a solid which maybe molded into particles having large surface area in order to enhanceits efiiciency in the desalinization process.

Another modification of the composition and structure of the ionretention agent, particularly applied when the premodified form is asubstance having a low melting point or when it is a water-solublematerial, is the variation in which some of the free amino acid groupsare condensed with a reactive ketone, preferably with an hydroxy ketonesuch as acetol (CH COCH OH), which undergoes condensation with the freeamino and free acid groups to form a product capable of chelating withthe electropositive and the electronegative ions of the salt in the feedstock solution. The amino carbonyl cross-linkage resulting from thecondensation between the amino group of the ion retention agent and thecarbonyl group of the modifying agent is formed via a mechanismsubstantially similar to the reaction represented by the following whichillustrates the modification of an amino acid containing a carboxylicacid group with acetone:

Compounds other than acetone which contain the reac tive keto groups andwhich preferably contain not more than five carbon atoms on either sideof the carbonyl radical form the above type of reaction product with theamino acid ion retention agent, as illustrated above, for

acetone, including such compounds as mesityl oxide, phorone,ditertiarybutylketone, acetylacetone, methylpropylketone, diethylketone,diacetylbenzene, diacetone a1- cohol, di-n-propyl ketone,diisopropylketone, etc. The condensation is generally effected byheating a mixture of the reactants, that is, the ketone with the aminoacid, to a temperature preferably from about 50 C. to about 200 C. andthereafter removing the excess ketone from the condensation product, forexample, by distillation or by extraction with a solvent such as Water.

Synthetic, resin-like ion absorption agents having dipolar or internalsalt structures are utilizable in the present desalinization process ineither of two major physical forms: (1) solid, water-insolublecross-linked polymers of unsaturated monomers containing both basicamino and acidic dipolar groups, as herein described; these polymers areuseful in a procedure in which the liquid saline solution is contactedwith a bed of solid particles of the ion retention agent or with asolution of the ion retention agent in a solvent immiscible with theaqueous feed stock solution, and (2) liquid organic compounds containingthe functional amino and acid groups as substituent polar radicals,having molecular weights sutficiently high (that is, above about 250)that the compound is substantially immiscible with the feed stocksolution, either individually or in solution in a solvent itselfimmiscible with saline feed stock solutions. Such liquid ion retentionagents or a solution of the composition in a liquid solvent are used ina process flow equivalent to a liquid-liquid extraction procedure, forexample, under countercurrent flow conditions and preferably in anarrangement in which one of the phase is dispersed as liquid droplets inthe other liquid phase, as shown in U.S. Patent No. 2,746,846 issued toG. R. Grunewald et al.

The aforementioned solid resinous polymers which may be convenientlyutilized either in a particulate solid form or dissolved in a liquidsolvent immiscible with the feed stock solution are prepared by thepolymerization of ethylenically unsaturated amino acids. The term:ethylenic unsaturation is intended to designate the presence of amono-olefinic double bond in an aliphatic substituent present in themolecular structure of the monomer enabling the monomer to undergointerpolymerization with another ethylenically unsaturated monomer ofthe same or different composition. Typical utilizable unsaturatedmonomers which polymerize to form solid, resin-like copolymers atappropriate polymerization conditions include, for example, thefollowing: the various ortho-, metaand para-vinyl-substitutedaminosulfonic acid derivatives of benzene, including thevariousside-chain position isomers and especially and more preferably,the isomers in which the sulfo and amino groups are substituted oncarbon atoms of the ring separated by at least one nuclear carbon atom,such as 2-amino-4-sulfo-styrene, Z-amino-S- sulfo-styrene,2'amino6-sulfo-styrene, 3-amino-5-sulfostyrene, 4-amino-6-sulfo-styrene,3-amino-6-sulfo-styrene, 3-amino-5-sulfo-alphamethyl styrene, and themeta, sulfoand para-sulfo-N-viny1-anilines and more preferably, asaforesaid, the isomers in which the sulfo group is para to the aminogroup. Another general group of compounds utilizable herein as thepolymerizable monomers for the formation of the ion retention agentshereof are the styrene derivatives containing substituent amino andcarboxyl radicals which are substituted either on the aromatic nucleusor in an alkyl substituent radical, including all of the variousposition isomers as well as the N-vinyl-aminobenzoic acids, such as2-amino-4-carboxystyrene, 3-amino-5- carboxystyrene,2-arnino-5-carboxystyrene, 4-amino-2-carboxystyrene or4-amino-6-carboxystyrene, 3-amino-6-carboxystyrene,Z-amino-6-carboxystyrene, 3-(N-vinyl)-benzoic acid, 4-(N-vinyl)-benzoicacid, and especially the isomers in which the nuclear carbon atomscontaining the carboxyl and amino substituents are separated by at leastone intervening carbon atom, represented, for example, byS-amino-S-carboxystyrene, and the metaand para- N-vinylamino benzoicacids. Still another group of polymerizable monomers which, togetherwith a copolymerizable diene, forms a solid copolymer resinous ionretention agent of the present invention are the taurines and taurinehomolgs: N vinyl-taurine-(N-vinyl-2-amino-ethanesulfonic acid), as wellas 3-amino-propanesulfonic acid, 4- aminobutanesulfonic acid,3-aminobutanesulfonic acid, 5- aminopentanesulfonic acid,4-aminopentanesulfonic acid, alpha-aminoacrylic acid,alpha-aminobutenoic acid, betaaminobutenoic acid, and compounds ofsimilar structure in which the carboxyl and amino groups are substitutedon carbon atoms separated by at least one, up to five and morepreferably not more than three intervening carbon atoms.

Polymers of unsaturated amino acids of the type hereinabovecharacterized, either individually or in admixture with otherunsaturated monomers which form copolymer linkages with the unsaturatedamino acid monomer have a greater tendency to be water insoluble, ifcopolymerized with a crosslinking agent selected from the groupconsisting of aldehydes and ketones as hereinbefore set forth. Thepolymerization is generally effected at a temperature of from about 10to about 300 C., depending upon the reactivity of the monomers. Whenutilizing a cross-linking agent, such as acetole, for the purpose ofincreasing the water-insolubility and melting point of the resultingcrosslinked polymeric resin, intermediate temperatures in the range ofabout 50 C. to about 200 C. are employed. The concentration ofcross-linking agent is such that the molar ratio of unsaturated aminoacid to cross-linking agent is in the range of from about 5:1 to about2:1.

Since most of the ion retention capacity of the present resins residesin the surface of the ion retention agent (liquid droplet or solidparticle) in contact with the aqueous feed stock solution, the salt ionsin the aqueous phase being generally incapable of migrating more deeplyinto the resin structure than the acid and the amino groups on oradjacent to the surface of the particle, the capacity of a given weightof resin for ion retention is dependent upon, among other factors, thestate of subdivision of the ion retention agent. The effective ionretention surface of a given weight of the ion retention agent issubstantially increased by dissolving the resin or polymeric ionretention agent in a solvent for the resin or polymer, and coating thesurfaces of a mass of solid particles of a suitable adsorbent material,such as charcoal, alumine (bauxite), sand, silica gel, or otherparticles of inert, water-insoluble, preferably porous, material withthe resulting solution of the resin and thereafter evaporating thesolvent from the particles suffused or impregnated with the solution,leaving a layer of the ion retention agent on the surfaces of theparticles. The ion retention agent ultimately fabricated by impregnationof the inert support particle should preferably contain at least 3percent by weight of the active ion retention agent.

Another alternative modification of the ion retention agent utilizablein the process of the present invention, employing another variation inthe method of contacting the aqueous feed stock solution with the ionretention agent, is represented by the formation of tailor-made aminoacid molecules which contain large, hydrophobic hydrocarbon groups. Theresulting amino acids generally exist in the form of liquids,semi-solids or solids. These ion retention agents are effective whendissolved in an inert solvent which is immiscible with the aqueous feedstock solution, or, if the product is a liquid, the ion retention agentis used directly in a liquid-liquid extraction procedure, with theaqueous feed stock as one of the liquid phases and the liquid amino acidas the other phase. Conventional countercurrent methods of contactingthe aqueous feed stock solution with the ion retention agent immiscibletherewith may be advantageously used to enhance the efiiciency of theprocess.

Liquid ion absorption agents of the foregoing type for use in a processflow similar to conventional solvent extraction procedures, in which theliquid contains the ion retention agent (either individually ordissolved in a non aqueous, immiscible solvent), are characteristic ofseveral distinct classes of compounds, including the longchain alkylamino sulfonic acids, (also referred to as N-alkyltaurines), preferablycontaining the amino and sulfo substituents on carbon atoms separated byfrom one to five intervening carbon atoms, compounds having thestructure of the N-alkylalanines, the N-alkyl-ortho-aminobenzenesulfonic acids and compounds of similar structure in which the N-alkylgroups contain a sufiicient number of carbon atoms, generally from tento about thirty per molecule, to render the resulting compoundwaterinsoluble, but oil soluble. Typical illustrative examples of suchcompounds are N-dodecyl-3-aminopropane sulfonic acid,N,N-dioctyl-3-aminopropane sulfonic acid, N-octadecyl-N-methyl-taurine,N-dodecylbenzyl-3-aminopropane sulfonic acid,N-octylcyclohexy1-3-aminopropane sulfonic acid, N-tridecyl-alanine,N,N-didodecylalanine, N-dodecyl-N-butyl-m-amino-benzene sulfonic acid,N- dodecyl-n-aminobenzene sulfonic acid, 3-dodecyl-5-aminobenzoic acid,3-amino-4-tetradecylbenzoic acid, N-dodecyl-p-aminobenzene sulfonicacid, etc.

The ion retention stage of the present process cycle is effected at thelowest temperature provided in the process cycle, herein referred to asthe datum temperature, generally at a temperature of from about to about40 C., or at whatever ambient temperature the feed stock solution isavailable for supply to the process. Thus, sea water is generallysupplied or available at a tempera ture level maintained during theprocess at which maxisorption takes place readily and rapidly. Theso-called elevated temperature of the present cycle, or the temperaturelevel maintained during the process at which maximum desorption of saltfrom the spent resin takes place, is generally a temperature within therange of from about 50 to about 100 C., and more preferably from about70 to 95 C. at atmospheric pressure, up to about 120 C. at from 10 toatmospheres pressure.

The following examples describe and illustrate several typical ionretention resins of this invention. In each instance the resin is testedfor its ion retention capacity by the following procedure which, becauseit is uniformly applied to all samples tested, is a measure of therelative effectiveness of these samples:

TEST METHOD The following runs describe processes for the desalinizationof sea water, the deionized product containing from 10 to about 1000ppm. of dissolved solids, depending upon the particular ion retentionagent utilized in the run. The sea water used as feed stock is asolution containing about 3.3% by weight of dissolved solids consistingmostly of sodium chloride, but which also contains significantproportions of other soluble salts, such as the halides, carbonates andsulfates of such metals as calcium, magnesium and potassium. The seawater is supplied to the process at a temperature of about 8 C. flow ingdirectly at this temperature into the top of a vertical column containedin a tube of approximately 2 inches diameter by 3 feet in height packedwith the particles of resin undergoing test. The particles of resin aresupplied in a variety of sizes to observe the efiect of particle size onthe capacity of the resin compared on a weight for weight basis. As thesea water feed stock fiows through the column of resin particles,deionized water product issues from the bottom of the ion retentioncolumn and the flow of sea water is continued until chloride ions appearin the efiiuent. The capacity of the resin is determined on the basis ofthe quantity of sea water treated and the quantity of dissolved solidsremaining in solution in the eflluent ratfinate. In the case of theliquid ion retention agents (liquid, that is, at the sea Water inlet ordatum temperature of 8 C.) a weighed quantity of the liquid ionretention agent is placed in a one liter flask and shaken with a givenquantity of sea water. Deionized water product is decanted from theupper layer of liquid ion retention agent after settling and theprocedure is thereafter repeated with the same sample of liquid ionretention agent until the organic phase becomes saturated with salt ionsand fails to further remove dissolved solute from the next aliquot ofsea water feed stock. The solid ion retention agents, in their spentform, are regenerated and their salt content removed to form areactivated material by first mixing the deactivated or spent ionretention agent with sea water at C. to partially remove the saltretained by the ion retention agent to an equilibrium concentration ofsodium chloride in the solid and solution phases and thereafter theresulting, partially reactivated ion retention agent is furthercontacted with deionized water at 90 C. to remove substantially all ofthe remaining salt ions from the ion retention agent. The resultingreactivated ion retention agent is recycled for use in a succeeding run.

EXAMPLES The following specific ion retention agents, indicating theirmethod of preparation and their physical properties are described asfollows:

Example I.Ion retention resin A A mixture of 10 molar proportion of thesodium salt of 3-carboxy-6-amino styrene per molar proportion ofdiacetyl benzene are polymerized by the emulsion technique using benzoylperoxide (0.96% by weight of the sodium salt or 1.78 weight proportions)as catalyst for the resulting copolymerization reaction. The carboxylsalt and the diacetyl benzene are initially emulsified in a rockingautoclave containing 75 volumes of an aqueous 0.5 percent solution ofsodium oleate. After mixing in the autoclave for 15 minutes with thesoap solution at 60 C., the monomers form a milky emulsion in theaqueous soap solution. The action of the autoclave is thereaftertemporarily interrupted to charge benzoyl peroxide into the emulsion,followed by continuing the rocking action of the autoclave reactor foran additional 35 minutes. During the resulting polymerization, a mass ofhard, amorphous solid particles of approximately spherical form and in asize range of from about 0.5 to about 2.5 millimeters in diameterseparates from the aqueous phase.

The formed particles of polymer are thereafter filtered from the aqueousphase, washed with water and heated in the presence of three volumes ofdistilled water to a temperature of about C.; that is followed bydraining the resulting aqueous phase from the container at the boilingpoint of water, replacing the aqueous phase with an additional threevolumes of distilled water and again boiling the mixture of water andresin particles. After five successive treatments with boiling water ina manner similar to the above, the aqueous filtrate from the treatedresin is substantially free of sodium ions and the recovered resin ispacked into the ion adsorption column described above.

Example 1I.Ion retention agent B A C amino acid is formed by a sequenceof reaction steps in which decene-l (formed by dehydrobromination ofdecylbromide) is initially reacted with phosgene (carbonyl chloride) andhydrogen chloride in the presence of anhydrous zinc chloride catalyst(2% by weight of the N-decene-l) in a condensation reaction effected ina stirred pressure autoclave at C. and at a pressure of hydrogenchloride maintained at 10 atmospheres, the resulting product consistingpredominantly of l-chloro-formyl-2-chlorodecane. The chlorocarbonylgroup is hydrolyzed to the corresponding sodium carboxylate radical byheating the foregoing chlorocarbonyl derivative in an autoclave at 10atmospheres pressure and at C. with a 10% aqueous caustic solution.

The resulting sodium salt of the monochloroundecanoic acid is thereaftercondensed With an equimolar proportion of 1-chl0ro-2-nitrobutane bymixing the undecanoic acid derivative and the chloronitrobutane with twomolar proportions of finely powdered magnesium and heating the mixturein a rotating autoclave containing nitrogen at 50 atmospheres pressure,at a temperature of 80 C. as the autoclave is slowly rotated during areaction period of approximately three hours. The product which ispredominantly 3-nitro-5-carboxymethyltridecane is thereafter mixed withfinely divided nickel sulfide (2% by weight of the nitro compound) in anautoclave which is thereafter charged with hydrogen to a pressure of 20atmospheres and heated for three hours at a temperature of 60 C. as theautoclave is slowly rotated to effect intimate mixing of nickel sulfidecatalyst with the salt of the pentadecanoic acid derivative. Aftercooling the autoclave and recovering the organic product from theinorganic material in the autoclave by elution with 95% ethanol, thealcohol extract is evaporated to drynessand the residue consisting ofthe sodium salt of the aminopentadecanoic acid is heated in a pressureautoclave with slightly acidified water at 110 C. followed by extractionof the resulting C amino acid, with dodecane.

The extract solution of the C amino acid and dodecane is admixed withacetol in a molar ratio of about 15: 1, and reacted under condensationconditions by the emulsion technique previously described in Example I.The mass of hard solid particles, substantially spherical in shape, andhaving a size ranging from approximately 0.5 to about 2.5 millimeters(nominal diameter) are filtered from the liquid phase and washed withwater until the aqueous phase from the filtrate is substantially freefrom sodium ions. The recovered cross-linked resin is then subjected tothe ion adsorption test, method hereinbefore set forth.

The results of the test method are presented in the following table:

TABLE L-DESALINIZATION OF SEA WATER BY CONTACT WITH ION RETENTION AGENTSea water treated Residual solids Restoration of ion i As ldentlfied andcharacterized in the foregoing descript As indicated by the appearanceof sodlum chloride in the ratfinate efiiuent and based on the quantityof supported material (i.e.. support plus ion retention agent) presentin the phase contacted with the feed stock (sea water).

Average of ten successive desorption-regeneration procedures on the samesample of ion retention agent.

Measure of the solids content of the last 100 cc. of the raffinateeffluent withdrawn from the spent ion retention agent; the solidscontent of the first cc. of rafiinate is, in each instance, nil.

The foregoing specification, and the examples presented therein, clearlyillustrates the use of the ion-retention agents of the present inventionin the desalinization of sea water, and indicates the benefits affordedthrough the utilization thereof.

I claim as my invention:

1. A solid organic water-insoluble cross-linked polymer havingheat-reversible ion retention capacity for-med by reacting an aminocompound with a ketone at polymerization-condensation conditions, saidamino compound being selected from the group consisting of (1)monocyclic aromatic amino compound containing a nuclearly attached aminogroup, an acid group and an ethylenically unsaturated aliphatic radical,the acid group thereof being sulfonic or carboxyl and being substitutedon a nuclear carbon atom separated from the nuclear carbon atom hearingthe amino group by one or two intervening carbon atoms and (2) aliphaticethylenically unsaturated amino compound containing an acid group inwhich the acid group is sulfonic or carboxyl and is substituted on acarbon atom separated from the carbon atom bearing the amino group byfrom one to three intervening carbon atoms.

2. The polymer of claim 1 further characterized in that said ketone isacetol.

3. The polymer of claim 1 further characterized in that said aminocompound is an aliphatic ethylenically unsaturated carboxylic aminoacid.

4. The polymer of claim 1 further characterized in that said aminocompound is a benzene compound containing a nuclear vinyl radical.

5. A process for the desalinization of an aqueous solution of adissolved salt which comprises: contacting said solution at a low datumtemperature with an ion retention agent comprising the water-insolublepolymer of claim 1, substantially each acid group of the polymeradjacent to an amino group of the polymer forming a dipolar aggregatewhich on contact with said solution with draws the electropositive andelectronegative ions of the salt from the solution, and forms aresulting complex between the acid and amino groups in the ion retentionagent with the electronegative and electropositive ions of said salt,and withdrawing at said datum temperature, from the ion retention agentcontaining absorbed thereon the salt ions originally present in saidsolution, a water product in which the concentration of salt is lessthan the salt concentration of said solution.

6. The process of claim 5 further characterized in that the activity ofthe ion retention agent, for further use in contacting additional feedstock solution, is restored by contacting the ion retention agent,containing absorbed thereon the salt ions withdrawn from said solutionin the ion retention stage of the process, with water at a temperaturerelativelymore elevated than said datum temperature and removing at saidelevated temperature a desorhate effluent of higher salt concentration,than said feed stock solution, from the resulting regenerated ionretention agent.

7. The process of claim 5 further characterized in that said polymer isprepared from a monocyclic aromatic amino acid containing anethylenically unsaturated aliphatic radical.

8. The process of claim 5 further characterized in that said polymer isprepared from an aliphatic ethylenically unsaturated amino acid.

References Cited UNITED STATES PATENTS 2,275,210 3/1942 Urbain et a1.2l0-37 3,078,140 2/1963 Hatch -1 210-38 X 3,205,184 9/1965 Hatch 210-37X OTHER REFERENCES Report No. 27; Saline Water Conversion; Advances inChemistry Series; American Chemical Society; Washington, D.C., 1960; pp.50-53 relied on.

REUBEN FRIEDMAN, Primary Examiner. C. M. DITLOW, Assistant Examiner.

US. Cl. X.R. 210-38, 37; 260-78, 79.3, 89.7

